Design and evaluation of a 6.6 kW GaN converter for onboard charger applications

This paper presents a compact, lightweight, highly efficient, 6.6 kW isolated three-port dc-dc converter for onboard charger (OBC) applications. The converter was designed and fabricated using normally-off gallium nitride (GaN) transistors; a three-dimensional (3-D) printed cold plate; high-voltage heavy copper printed circuit board (PCB) power planes; low-voltage (14 V) and high-current PCB power planes; and a planar transformer. The prototype has a power density of 10.5 kW/L and specific power of 9.6 kW/kg. Test results show greater efficiency than a silicon-based counterpart, even at 2.5 times higher switching frequency. The isolated GaN converter was integrated with a 100 kW segmented traction inverter that uses silicon carbide MOSFETs and 3-D printed components to test the functionality as a level-2 OBC. Testing and evaluation of the integral onboard charging functionality was successfully completed at power levels up to 6.6 kW.